This invention is related to acoustical or ceiling panels. More specifically, this invention relates to acoustical panels that have less bound water, and are therefore easier to dry than conventional panels.
Acoustical tiles, also known as acoustical panels, ceiling tiles or ceiling panels, are well known in the building trades for providing a ceiling that is quickly installed, inexpensive and lightweight. The tiles are prepared from a slurry of fillers and binders, most frequently by either a casting process or a water felting process.
In the water felting of such a slurry, a dispersion of fibers, binders, and other ingredients flow onto a moving, porous support, such as that of a Fourdrinier or Oliver mat forming machine for dewatering. The dispersion is dewatered first by gravity and then by pressing and vacuum suction means. The wet basemat is dried in heated convection drying ovens and the dried material is cut to the desired dimensions, fissured and/or perforated to impart acoustical absorbency and optionally top coated, such as with paint, to produce acoustical tiles and panels.
Acoustical tile is also made by a wet pulp molded or cast process such as that described in U.S. Pat. No. 1,769,519. A molding composition that includes fibers, fillers, colorants and a binder is prepared for molding or casting the body of the tile. This mixture is placed upon suitable trays which have been covered with paper or a paper-backed metallic foil and then the composition is formed to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the pulp are then placed in an oven to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into panels of a desired size.
Fillers that are very lightweight are preferred for use in the making of acoustical tiles because they act as a bulking agent thus contributing to a lower density and overall lighter product. This lighter final product is desirable because it lessens shipping weight and provides for ease in handling and installation. Expanded perlite is a preferred filler material because it provides bulking and is lightweight.
Expanded perlite has an internal structure that consists largely of interconnecting open cells. This structure leads to the absorption of water into the interior of the perlite particles by capillary action. It has been found that the water in the acoustical ceiling tile dispersion is present essentially in two modes. Free water is defined as water which can be removed mechanically from the furnish, including drainage through the wire, with and without vacuum, and through the press section of the process. Bound water is defined as water that is contained within the interior of the particles particularly the perlite particles either by hydrogen bonding or capillary action, and which cannot be removed mechanically, such as by suction or pressing. This bound water can be driven off by heating the basemat to increase the partial pressure of water, driving it from the basemat. However, heating the basemat and all of the water held in the pores is relatively expensive, particularly when the high price of fossil fuels is considered. The water retention value (“WRV”) is defined as the weight of the bound water as a percentage of the dry weight of the sample.
The use of silicone compounds are known for treating expanded perlite to reduce the amount of bound water present in the basemat. U.S. Pat. No. 5,964,934, herein incorporated by reference, describes an acoustical panel that utilizes expanded perlite that has been treated with silicone polymers, siloxanes, reactive silane monomers and other silicon compounds to reduce the bound water. However, there are several disadvantages to using silicone compounds to treat perlite. Silicone polymers are expensive. They cost almost four times the cost of typical thermoplastic polymers. There are also handling and health related hazards associated with the use of silicone polymers. Also, there are detrimental effects on the physical properties of the panels as a result of treating the perlite with a silicone coating. Approximately 20% of the strength of a panel is typically lost when silicon compounds are used to coat expanded perlite. Commercially available silicon treated perlite (STP) is extremely difficult to wet and to disperse in water, making them difficult to blend into the slurry.
There is a need for a treatment of expanded perlite to reduce the amount of bound water present in acoustical panels. The treatment must be effective in reducing the water that is absorbed into the pores of the perlite particles but should permit the treated perlite to mix into the slurry and wet out easily. Hazards and cost of the treatment should be reduced and the physical properties of the resulting panels should not be negatively affected.